Read a whole text file into a MATLAB variable at once

Question

I would like to read a (fairly big) log file into a MATLAB string cell in one step. I have used the usual:

s={};
fid = fopen(\'test.txt\');
tline = fgetl(fid);
w         


        

Answer 1

The main reason your first example is slow is that s grows in every iteration. This means recreating a new array, copying the old lines, and adding the new one, which adds unnecessary overhead.

To speed up things, you can preassign s

%# preassign s to some large cell array
s=cell(10000,1);
sizS = 10000;
lineCt = 1;
fid = fopen('test.txt');
tline = fgetl(fid);
while ischar(tline)
   s{lineCt} = tline;
   lineCt = lineCt + 1;
   %# grow s if necessary
   if lineCt > sizS
       s = [s;cell(10000,1)];
       sizS = sizS + 10000;
   end
   tline = fgetl(fid);
end
%# remove empty entries in s
s(lineCt:end) = [];

---

Here's a little example of what preallocation can do for you

>> tic,for i=1:100000,c{i}=i;end,toc
Elapsed time is 10.513190 seconds.

>> d = cell(100000,1);
>> tic,for i=1:100000,d{i}=i;end,toc
Elapsed time is 0.046177 seconds.
>> 

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EDIT

As an alternative to fgetl, you could use TEXTSCAN

fid = fopen('test.txt');
s = textscan(fid,'%s','Delimiter','\n');
s = s{1};

This reads the lines of test.txt as string into the cell array s in one go.